<template>
	<ul class="list">
		<li class="item" v-for="item of letters" :key="item" @click="handleLetterClick" @touchstart.prevent="handleTouchStart" @touchmove="handleTouchMove" @touchend="handleTouchEnd" :ref="item">{{item}}</li>
	</ul>
</template>
<script>
export default{
	name:'CityAlphabet',
	props:{
		cities:Object
	},
	computed:{
		letters(){
			const letters=[]
			for (let i in this.cities) {
				letters.push(i)
			}
			return letters
		}
	},
	data(){
		return{
			touchStatus:false,
			startY:0,
			timer:null
		}
	},
	updated(){
		this.startY=this.$refs['A'][0].offsetTop
	},
	methods:{
		handleLetterClick(e){
			this.$emit('change',e.target.innerText)
		},
		handleTouchStart(){
			this.touchStatus=true
		},
		handleTouchMove(e){
			if(this.touchStatus){
				if(this.timer){
					clearTimeout(this.timer)
				}
				this.timer=setTimeout(()=>{
					const touchY=e.touches[0].clientY-79
					const index=(touchY-this.startY)/20
					if(index >= 0 && index < this.letters.length){
						this.$emit('change',this.letters[index])
					}
				},16)
			}
		},
		handleTouchEnd(){
			this.touchStatus=false
		}
	}
}
</script>
<style lang="stylus" scoped>
@import '~styles/varibles.styl'
	.list{position:absolute;top:1.58rem;right:0;bottom:0;width:0.4rem;display:flex;flex-direction:column;justify-content:center;}
	.item{text-align:center;line-height:0.4rem;color:$bgColor;}
</style>